In a mobile body communication system such as PHS (Personal Handyphone System), mobile phone systems, etc., a simultaneous call is made across a plurality of base station devices as a single paging area, and a call accepting sequence is started between a mobile station device such as a PHS and a mobile phone and a base station device that received a response from the mobile station device.
In such a mobile body communication system, the plurality of base station devices are associated with the same number indicating the single paging area, so that the station devices are treated as constituting one paging area. In the HLR (Home Location Register) provided in the mobile body communication system, mobile station devices and the numbers are registered in association with one another. At the time of making a call, an exchange at the transmitting party or a gateway exchange device upon receiving a call from another network reads the associated number of the mobile station device as the receiving party by referring to the HLR and a simultaneous call is made in at least one base station device corresponding to the number.
Meanwhile, IP telephone adapted to VoIP (Voice Over Internet Protocol) that utilizes a protocol on an IP network such as SIP (Session Initiation Protocol) has come to receive much attention. In mobile body communication, a wireless LAN (Local Area Network) based on SIP has been tested using a PDA (Personal Digital Assistance) or a dedicated terminal as a mobile station device.
With such IP telephone, the mobile station device on the receiving side is identified by specifying the IP address by the transmitting side or if the IP address is stored in the SIP server on the Internet or the LAN in association with the telephone number or mail address, the transmitting side designates the telephone number or the mail address to read out the IP address corresponding to the telephone number by referring to the SIP server and specifies the IP address. Then, the call is received by IP routing.
Application of the above described VoIP technology to the conventional mobile body communication system described above can eliminate the need for the exchange or allows lines to be more efficiently used, which could reduce the communication cost. In addition, as a backbone IP network has been developed and the VoIP techniques have been improved, adaptation in IP of existing mobile body communication systems have been researched and developed.
In the disclosure of Patent Document 1, a voice call is converted into data packets during voice communication between a mobile body communication network connected to a commination network based on an internet protocol and a mobile station.
Patent Document 1: JP-T-2001-527337